The present invention relates to sacral implants, and more particularly to an improved implant system for fixing a stabilizing appliance to the sacrum and to the lumbar vertebrae.
Spinal fusion, especially in the lumbar and sacral region is regularly employed to correct and stabilize spinal curves, to prevent recurrence of spinal curves and to stabilize weakness in trunks that result from degenerative discs and joint disease, deficient posterior elements, spinal fracture, and other debilitating problems. Spinal implant systems have been used regularly to stabilize the lumbar and sacral spine temporarily while solid spinal fusions develop.
Several temporary stabilization systems are currently in use. All perform adequately, however leave room for improvement. For example, an implant system for attaching the superior most lumbar vertebra (L1) to the implant without interfering with normal motion of the next superior vertebra needs to be developed. Additionally, implant systems that achieve stronger sacral fixation, easier use for multiple segment fixation, and easier use with spinal deformity are needed. Further, better implant systems for rigidly tying the base of the system to the sacrum must be developed.
The present invention provides a sacral implant system that rigidly affixes the base of the implant system to the sacrum while allowing ease of installation and flexibility of design. Moreover, the present system provides apparatus for securing the upper portion of the implant system to, for example, the L-1 vertebra, without interfering with the next superior most vertebra (T-12) and any or all vertebrae in between. The sacral implant system of the present invention comprises first and second sacral plates for mounting on opposite sides of the sacrum adjacent the lumbosacral junction. Each of the sacral plates has at least a pedicle and oblique mounting means for rigidly affixing each of the sacral plates to the sacrum. The system also includes first and second rods extending in a superior direction and generally parallel relationship from respective ones of the sacral plates. The rods are situated on opposite sides of the sagittal plane. Means are also provided for rigidly affixing the rods to respective sacral plates. At least one connecting member is employed to rigidly interconnect the rods at a location superior to the sacral plates. Finally, a superior fixation plate having a lateral portion and a medial portion is employed to affix the superior most vertebra to be fused to the implant system. A pedicle screw is fixed to and through the pedicle of the vertebra. The lateral portion of the fixation plate is rigidly affixed to the pedicle screw. The medial portion of the fixation plate is offset in an inferior direction sufficiently far so that it avoids the inferior articulate process of the next superior vertebra. In this manner the next superior vertebra can move in a normal fashion relative to the vertebra to be fused during the temporary stabilization. Preferably, a lateral fixation plate is also used for pedicle fixation of intermediate vertebrae.
In another aspect of the invention, a specialized pedicle screw is provided for attachment of the offset and lateral fixation plates to the vertebra. The screw includes a first threaded portion for threading into the vertebra, a subhead portion and a second threaded portion projecting above the subhead. The second threaded portion is adapted to receive a nut. The subhead has a diameter greater than the second threaded portion and an upwardly facing shoulder lying in a plane substantially orthogonal to the axis of the screw. In use, the shoulder engages the anterior surface of the fixation plate while the nut is threaded on the second threaded portion and bears down against the posterior surface of the plate to secure the plate and screw together.